The effects of a 4-day inhalation exposure to methyl isocyanate (MIC) on bone marrow parameters in female mice were examined. The MIC exposure was associated with myelotoxicity as evidenced by hypocellularity, suppression of pluripotent stem cells (CFU-S), granulocyte macrophage progenitors (CFU-GM) and erythroid precursors (CFU-E) in both dose groups.